Regulated bias voltage supply



Feb. 19, 1957 M. SISKEL REGULATED BIAS VOLTAGE SUPPLY Filed Dec. 1953IXIfENTOR. MANUEL v SISKE-L A TTOR NE Y and H 2,782,340 REGULATED BIASVOLTAGE SUPPLY lvianuel Siskel, Camden, N. J5, assignor to RadioCorporation of America, a corporation of Delaware Application December29, 1953, Serial No. 400,963

7 Claims. on. 3-15-30 This invention relates generally to regulated biasvoltage supplies, and more particularly to a regulated bias voltagesupply for cathode ray tubes supplied with operatingpotentials fromnegative output high voltage power supplies. While neither specificallynor eXclusively limited thereto, the regulated bias voltage supply ofthe present invention'is particularly useful for supplying a fiXed biasvoltage at a low impedance for cathode ray tubes in applications whereit is necessary to clamp incoming signals to the bias level voltage forD. C. restoration purposes.

There are many instances in the commercial applications of cathode raytubes where it is either necessary or desirable to apply a grounded orvery low voltage to the anode, and'a high negative voltage to thecathode. The grid bias voltage in these, cases is normally obtained froma variable tap on a resistive voltage divider network. In most of thesecases, the resistive voltage divider network is in the order ofmanymegohms so that the grid bias voltage is effectively derived from arelatively very high impedance source. This very high impedance sourceis objectionable where it is necessary to clamp incoming signals appliedto the control grid of the cathode ray tube to the bias voltage levelfor D. C. restoration purposes, as is usually the case.

It is, therefore, a principal object of the present invention to providean improved regulated bias voltage power supply at low impedance.

Another object of the present invention is to provide improved means forsupplying grid bias voltage at low impedances from a high impedancevoltage divider tap.

A further object of the present invention is to provide an improvedregulated low impedance bias voltage supply without the need foradditional transformers, rectifiers, or filters.

It is still a further object of the present invention to provide animproved low impedance regulated bias voltage power supply which issimple in structure and operation, economical and easy to manufacture,and highly efiicient in use.

These and'further objects of the present invention are attained in animproved regulated bias voltage supply having a high'input impedance anda relatively low output impedance. A regulated bias voltage supply, inaccordance with the present invention, is a part of the output voltageof a negative output high voltage power supply. A high resistive voltagedivider network is connected across the negative and positive outputterminals of the negative output high voltage power supply, and thepositive terminal thereof is grounded. A portion of the voltage divideradjacent the negative terminal of the high voltage power supply ismaintained at a constant voltage by one or more voltage regulating tubesconnected in parallel therewith. A triode and a cathode resistortherefor are also connected in parallel with the portion of the voltagedivider maintained at a constant potential. One end of the cathoderesistor is connected'to the negative output terimnal of the negativeoutput high voltage power rates Patent supply. The grid of the triode isconnected to an adjustable tap on the portion of the resistance of thevoltage divider that is maintained at a constant potential. The outputof the regulated bias voltage supply is derived from the anode and thecathode of the triode. in practice, the anode of the triode will beconnected to the cathode of a cathode ray tube and the cathode of thetriode will be connected to the control grid of the cathode ray tubethrough a grid resistor. Where input signals to the grid of the cathoderay tube are to be restored to the bias level voltage applied to thegrid resistor, the anode of the diode is connected to the cathode of thetriode. With this arrangement, any tendency causingthe grid voltageapplied to the cathode ray tube to rise, which may be caused by anincreased positive input signal to the grid of the cathode ray tube,will be offset by an increase in the internal impedance of the triodewhich, in turn; will tend to decrease the flow of current through thecathode resistor of the triode, thereby maintaining the cathodepotential thereof substantially constant. A reverse set of conditions,which may be caused by a high negative signal applied to the input ofthe cathode ray tube, tending to lower the grid bias, will be offset bya decrease in the variable impedance of the triode, which in turn, willtend to cause more current to flow through the cathode resistor, therebytendingto restore the cathode voltage of the triode to its .originalvoltage. p

The novel features of:the present invention, as well as the inventionitself, both as to its organization and method of operation will beunderstood in detail from the following description when considered inconnection with the accompanying drawing, which is a scheniaticdiagramof a regulated bias voltage supply, connectedto a cathode ray tube in amanner to supply it with grid bias at a low impedance for D. C.restoration purposes, in accordance with the present invention.

Referring now to the drawing, there is shown a regulated bias voltagesupply which derives its energy from, and is a part of, a high voltagepower supply 10. The. high voltage power supply 10 may be any one of theconventional unidirectional output voltage types used for. the operationof cathode ray tubes, such as a regulated radio frequency power supply,a fiy-back type power supply, a regulated A. C. type using voltagedoubling circuits, and the like, well known in the art. A'positiveoutput terminal 12 of the power supply 10 is connected to a source ofreference potential, such as ground, thereby providing a negative outputvoltage. A negative output terminal 14 of the power supply It) isconnected to ground through a high impedancevoltage divider seriesnetwork 16 comprising a potentiometer 18, resistors 20 and 22, apotentiometer 24, and a resistor 26, connected in series. Constantvoltage means such as three voltage regulating tubes 28, 30 and 32,connected in series, are connected between the negative terminal 14 ofthe power supply 10 and the junction between the resistors 2i} and 22.The voltage regulating tubes 28, 30 and 32, which may be of the neontype or the like, serve to maintain the voltage across a portion of thevoltage divider network 16; namely, across the potentiometer 18 and theresistor 20, at a constant potential. One output terminal 34- of theregulated bias voltage supply is connected to the negative terminal 14of the power supply 10 through a 'resistor'36. The output terminal 3 3of the regulated bias voltage supply is connected to the junctionbetween the resistors 2d and 22, and to an anode of a variable impedanceelectron discharge device ill, such as a triode tube. The cathode of thetube 44} is connected to the output terminal 3 and the control grid isconnected to the movable tap of the potentiometer 18.

Means for maintaining the bias voltage across the terminals 34 and 38substantially constant will be eX- plained in connection with theoperation of a cathode ray tube 42 wherein it is necessary to clampincoming signals to the fixed voltage level at the terminal 34, for D.C. restoration purposes. The movable tap of the potentiometer 24 isconnected to a focus anode 44 of the cathode ray tube 42. Anaccelerating anode 46 of the cathode ray tube 42 is connected to ground.The cathode of the cathode ray tube is connected to the output terminal38 of the bias voltage supply, and the control grid 48 of the cathoderay tube 42 is connected to the output terminal 34 of the bias voltagesupply, through a grid resistor 50. Input signals are applied to thecontrol grid 48 of the cathode ray tube 42 through a coupling capacitor52, and are restored to the bias voltage level of the output terminal 34by clamping means such as a diode 54. The anode of the diode 54 isconnected to the output terminal 34, and the cathode of the diode 54 isconnected to the grid 48 of the cathode ray tube 42. The diode 54 may bereversed for limiting signals in an opposite polarity.

The operation of the regulatory action of the bias voltage supply, inaccordance with the present invention, will now be described inconnection with the operation of the cathode ray tube under conditionswhich tend to cause the bias voltage at the output terminal 34 to vary.The voltage applied to the control grid of the variable impedance tube40 in adjusted so that the tube 40 conducts suflicient current tomaintain the voltage at its cathode, that is, the voltage at the outputterminal 34, at a desired bias voltage level, without any input signalsapplied to the grid 48 of the cathode ray tube 42. It will be noted thatthe anode of the variable impedance tube 40 is maintained at asubstantially constant potential with respect to the negative terminal14 of the power supply because of the regulatory action of the voltageregulating tubes 28, 30 and 32. Let it now be assumed that a largepositive input signal is applied to the grid 48 of the cathode ray tube42. This positive signal will cause the cathode ray tube 42 to conductheavily. Conventional current may be said to flow from ground throughthe cathode ray tube 42 to its cathode, thence through the variableimpedance tube 40, the cathode resistor 36, to the negative terminal 14of the power supply 10. The increased current flow through the cathoderesistor 36 will tend to increase the voltage at the output terminal 34.The control grid of the variable impedance tube 40, however, ismaintained substantially constant since the portion of the voltagedivider 16 connected in parallel with the voltage regulating tubes 28,30 and 32 is maintained substantially constant. The tendency for thecathode of the variable impedance tube 40 to go positive has the sameeffect as increasing the negative bias of the variable impedance tube40, thereby causing the latter to decrease conduction therethrough, andalso through the cathode resistor 36. Thus, it is seen that a tendencyfor the voltage at the output terminal 34 to go positive, caused by thepositive-going signal applied to the grid 48 of the cathode ray tube 42,is offset by the tendency of the variable impedance tube 40 to increaseand thereby decrease the current through the cathode resistor 36,whereby the voltage at the output terminal 34 is maintainedsubstantially constant.

In the case where a strongly negative signal is applied to the controlgrid 48 of the cathode ray tube 42, there is a tendency for the voltageat the output terminal 34 to decrease in a negative direction because ofdecreased conduction through the cathode ray tube 42. Since the controlgrid of the variable impedance tube 40, however, is maintained at aconstant potential, the tendency for the cathode of the tube 40 to gonegative has the same effect as increasing the positive bias of thevariable impedance tube 40, resulting in a greater conductiontherethrough. An increased current through the variable impedance tube40 will cause more current to flow 4 through the cathode resistor 36,thereby increasing the potential at the output terminal 34, andofisetting any tendency of the voltage at the terminal 34 to drop.

Thus, it is seen that the shunted grid resistor 50 is connected to apoint, the output terminal 34, that maintains a substantially constantvoltage determined by the setting of the variable tap on thepotentiometer 13. Since the control grid 48 of the cathode ray tube 42is connected to a substantially fixed voltage at the output terminal 34,through the parallel circuit comprising the grid resistor 5t and thediode 54, the effect is the same as connecting the grid resistor 50 andthe diode 54 to a very low resistance in order to obtain effective D. C.restoration. In accordance with the bias voltage supply of the presentinvention, the grid resistor 50 may be relatively large compared withthe effective resistance of the bias supply, so that the ratio of gridresistance to bias supply resistance may be easily made as high as 1000,whereby D. C. restoration may be easily accomplished. It is noted thatwithout the regulated bias voltage circuit of the present invention, ifthe bias voltage for the cathode ray tube 42 were taken directly fromthe voltage divider network 16, a very high resistance, as is usuallythe case in prior art methods, D. C. restoration would not be assatisfactorily accomplished because of this high resistance. Thisfollows from the premise that good D. C. restoration may be had When thepath from the grid 48 of the cathode ray tube 42 to the negativeterminal 14 is one of high resistance when the diode 54 isnon-conducting, and one of relatively low resistance when the diode 54is conducting.

There has been shown and described, in accordance with the objects ofthe present invention, a bias voltage power supply for a cathode raytube. The input to the bias voltage power supply is a high impedancevoltage source derived from a portion of a conventional voltage dividernetwork of a high voltage power supply. The output of the bias voltagesupply presents a relatively low impedance whereby input signals appliedto the grid of the cathode ray tube may be restored to a substantiallyconstant regulated voltage at the output of the bias voltage supply.

What is claimed is:

l. A regulated bias voltage supply comprising a source of unidirectionalvoltage, a voltage divider network connected across said source, meansconnected across a portion of said network to maintain a constantpotential across said portion, a variable impedance tube having ananode, a grid and a cathode, a resistor connected between said cathodeand one end of said portion, said anode being connected to the other endof said portion, said grid being connected to a point on said portion,and output means to derive a regulated bias voltage output across saidanode and said cathode.

2. A regulated bias voltage supply comprising a source of unidirectionalvoltage, a voltage divider network connected across said source, meansconnected across a portion of said network to maintain a constantpotential across said portion, a variable impedance tube having ananode, a grid and a cathode, a resistor connected between said cathodeand one end of said portion, said anode being connected to the other endof said portion, said grid being connected to a point on said portion,and output means to derive a regulated bias voltage output across saidanode and said cathode, said one end of said portion being connected tothe negative side of said source of unidirectional voltage.

3. A regulated bias voltage supply comprising a source of unidirectionalvoltage, a voltage divider network connected across said source, meansconnected across a portion of said network to maintain a constantpotential across said portion, a variable impedance tube having ananode, a grid and a cathode, a resistor connected between said cathodeand one end of said portion, said anode being connected to the other endof said portion, said grid being connected to a point on said portion,and output means to derive a regulated bias voltage output across saidanode and said cathode, said source being a negative output voltagepower supply, and said one end of said portion being connected to thenegative side of said source.

4. Means for providing a cathode ray tube having a grid and a cathodewith a regulated grid bias voltage, said means comprising a source ofunidirectional voltage, a voltage divider network connected across saidsource, constant voltage means connected across a portion of saidnetwork, a circuit comprising a variable impedance device and a resistorconnected in series therewith, said circuit being connected in parallelwith said portion and said constant voltage means, said device having anelectrode connected to a point on said portion, and output means toderive said grid bias voltage across said device.

5. Means for providing a cathode ray tube having a grid and a cathodewith a regulated grid bias voltage, said means comprising a source ofunidirectional voltage, a voltage divider network connected across saidsource, constant voltage means connected across a portion of saidnetwork, a circuit comprising a variable impedance device and a resistorconnected in series therewith, said circuit being connected in parallelwith said portion and said constant voltage means, said device having anelectrode connected to a point on said portion, and output means toderive said grid bias voltage across said device, one end of saidportion and one end of said resistor being connected to the negativeside of said source of unidirec tional voltage.

6. Means for providing a cathode ray tube having a grid and a cathodewith a regulated grid bias voltage, said means comprising a source ofunidirection voltage, a voltage divider network connected across saidsource, constant voltage means connected across a portion of saidnetwork, a circuit comprising a variable impedance device and a resistorconnected in series therewith, said circuit being connected in parallelwith said portion and said constant voltage means, said device having anelectrode connected to a point on said portion, output means to derivesaid grid bias voltage across said device, one end of said portion andone end of said resistor being connected to the negative side or" saidsource of unidirectional voltage, and a grid resistor connected betweensaid grid and the other end of said first-mentioned resistor, saidcathode being connected to said device.

7. Means for providing a cathode ray tube having a grid and a cathodewith a regulated grid bias voltage in a manner to clamp signals appliedto said grid to the level' of said grid bias voltage, said meanscomprising a source of unidirectional voltage, a voltage divider networkconnected across said source, constant voltage means connected across aportion of said network, a circuit comprising a variable impedancedevice and a resistor connected in series therewith, said circuit beingconnected in parallel with said portion and said constant voltage means,said device having an electrode connected to a point on said portion,output means to derive said grid bias voltage across said device, oneend of said portion and one end of said resistor being connected to thenegative side of said source of unidirectional voltage, a grid resistorconnected between said grid and the other end of said firstrnentionedresistor, said cathode being connected to said device, and a diodeconnected across said grid resistor.

References Cited in the file of this patent UNITED STATES PATENTS2,219,188 Kuehni Oct. 22, 1940 2,394,891 Bowie Feb. 12, 1946 2,465,406Taylor Mar. 29, 1949 2,470,048 Norton May 10, 1949 2,559,078 Kell July3, 1951 2,629,840 Weiss Feb. 24, 1953

